While the mammalian superior colliculus is undoubtedly involved in many functions of which we know nothing about, it can be said that it does send control signals of some kind to brainstem and spinal cord systems concerned with eye and head position. The proposed studies are part of a long-range analysis of the basic pathways and circuitry which enable the colliculus to perform, or at least participate in these function(s). To reach this goal, neuroanatomical tracing methods will be used to explore the spatial relationships which exist between particular afferents to the superficial layers and the cells of origin of particular superficial collicular tectofugal systems. Emerging data indicate that collicular layers are divisible into sublayers on the basis of connectional and physiological criteria. Such sublaminae could be the sites of input-output linkages between particular afferents and efferents. Such a plan would allow different types of incoming information to distribute to select sets of collicular targets. Studies of the intermediate and deep layers will focus upon determining whether functionally related "patchy" inputs overlap and upon determining the local geometry of output systems. As part of our interest in collicular connectivity and function, we will study the geniculocortical components of a small-celled circuit over which fine-fibered retinal and tectal input reaches supragranular cortical layers. Finally, we will analyze the projection of the parabigeminal nucleus in the primate Macaca mulatta.